Technical Abstract:
The yield of gelatin extracted from fish skins depends on several factors, such as handling and storage conditions, and pretreatment, as well as washing and chemical dip conditions. Collagen from fish skins is usually degraded to gelatin by heat treatment at temperatures above 38°C. Power ultrasound treatment could be a promising method for such extraction as it facilitates cell and tissue disruption, potentially increasing gelatin extraction yield from previously frozen or dehydrated fish skins. Ultrasound treatment may also preserve gelatin quality.
The objective of the study was to evaluate the effects of power ultrasound as a processing aid in gelatin extraction on yield and quality of pollock fish gelatin from previously frozen and dehydrated fish skins.
Frozen and air-dried pollock skins were treated with cold saline, alkaline and acid solutions to separate collagen tissue and extract gelatin by collagen denaturation at 45°C for four hours with a power ultrasound treatment as a processing aid. The power ultrasound had two opposing magnetostrictive transducers at irradiation frequencies of 20 and 16 kHz operating on the Nearfield Acoustic Processor principle in a three-inch reaction cavity gap at 50% power. Gelatin yield, pH, clarity, gel strength and viscoelastic properties as well as molecular weight distribution determined by PAGE-SDS method were evaluated. Gelatin extracted in a water bath at 45°C for four hours was used as a control.
The power ultrasound treatment increased the extraction yield by 11.1% compared with the control while gel strength decreased 7%. Gelation temperature was also lower in ultrasound-extracted gelatin (4.2°C). This behavior is related to differences in molecular weight distribution of polypeptide coils in gelatins.
Power ultrasound extraction can be used to increase gelatin extraction from frozen and air-dried fish skins. This technology most likely will work as well to increase mammalian skin gelatin extraction.